Milk temperature and detection of oestrus in dairy cattle

Milk temperature was measured with the object of detecting oestrus in dairy cattle. Measurements were made in both experimental (well controlled) and commercial conditions. Milk temperature was measured twice daily during milking with an accuracy of ±0·1 °C. The milk temperature of two cows studied on the university farm increased by about 0·4 °C on the day of behavioural oestrus. On a commercial farm, milk temperature profiles were obtained for 18 post partum cows which exhibited a total of 34 periods of oestrus. Of these, 50% could be identified when the criterion used was a 0·3 °C elevation in milk temperature above the average for the previous 5 days (morning and afternoon profiles considered separately). However, an unacceptable fraction (81%) of the temperature spikes were false positives. In continuous temperature measurements, the body temperatures (vaginal) of two cows rose by about 0·5 °C at oestrus, but the increase in temperature lasted only about 9 h, and was less than 0·5 °C for much of this time. The twice daily measurement of milk temperature is not a reliable method of detecting oestrus in dairy cattle.